The invention pertains to a torsional vibration damper having a drive-side transmission element; a takeoff-side transmission element, which can deflect rotationally with respect to the drive-side element around an essentially identical axis of rotation; and a damping device, installed between the two transmission elements.
U.S. Patent Application Publication No. 2003/233907 discloses a torsional vibration damper wherein the drive-side transmission element is connected to a drive such as the crankshaft of an internal combustion engine, whereas the takeoff-side transmission element can be brought into working connection with a takeoff such as a gearbox input shaft by way of a clutch device, such as an engageable and disengageable friction clutch. So that torque can be transmitted between the drive-side transmission element and the takeoff-side transmission element, the damping device is provided both with a gas spring system, having a plurality of gas springs, and a supplemental spring system, containing a plurality of steel springs. When torsional vibrations occur, the steel springs are deformed and thus convert hard jolts into a softer vibration process in the known manner. The gas springs are responsible for a damping process which absorbs the energy of the jolts. For this purpose, each of the gas springs has a reservoir containing a gaseous medium such as air inside a cylinder space. When the gas spring is compressed and thus the volume of the reservoir is decreased, the gaseous medium is forced out of the reservoir through a throttle opening. Of course, when the load on the gas spring is released and thus the volume of the reservoir increases again, fresh gaseous medium is drawn back in from the environment through the throttle opening. This makes it possible to achieve velocity-proportional damping without any special sealing requirements.
The pressure in the reservoir and thus the damping behavior of the known gas spring system are the result of the deformation state at the moment in question. This gas spring system is therefore referred to in engineering circles as a “passive” system. The throttle opening is designed for all conceivable load states and therefore represents only a compromise. Steel springs suffer from the same problem, namely, that certain compromises must be made when adapting their spring characteristics to the different load states which occur during operation.
To remedy this problem in the case of steel springs, U.S. Pat. No. 5,307,710 describes the possibility of arranging a plurality of springs in a row in the circumferential direction and of providing the individual steel springs with different characteristics, so that, when small torques are introduced, only the steel springs with lower characteristics are compressed, whereas, when larger torques are introduced, the steel springs with the higher characteristics will be compressed as well. The problem here, however, is that steel springs are affected by the rpm's of the damper. That is, their turns are forced radially outward by centrifugal force, and they can then become immobilized in this radial position. Torsional vibrations therefore do not necessarily lead to the compression of the steel spring which is adjacent in the direction in which the torsional vibration is introduced, which means that the damping device may not provide any damping effect at all at first. Only an even higher load state will finally be able to break the steel spring loose from the radially outer immobilized position, which will be perceived in the vehicle as an unpleasant jerk. The circumferentially adjacent steel spring, however, which can be designed with a higher characteristic, will then also be deflected outward and initially immobilized until it, too, is broken loose from its radially outer contact position under the effect of an even higher load state. When a torsional vibration damper operates in this way, therefore, the overall result is that only a certain percentage of the spring system, never the entire volume, is available. The severity of this problem can be reduced but not eliminated by the sliding elements proposed in U.S. Pat. No. 5,307,710, which are inserted between the steel springs and their radially outer contact points. The quality with which torsional vibration dampers of this type isolate vibrations is therefore inadequate, and because of the high stiffnesses in the damping device, they have a resonance frequency in an rpm range which is present relatively often when a vehicle is being driven. Especially critical here is the lower range between 1,000 and 2,000 rpm when at the same time engine torques are high and the torsional vibrations which are being excited are correspondingly strong. Under such conditions, humming noises are heard in the vehicle.